Method and apparatus for battery-aware dynamic bandwidth allocation for wireless sensor networks

ABSTRACT

A method and apparatus that allocates bandwidth among wireless sensor nodes in a wireless sensor network (WSN) is disclosed. The method may include allocating transmission time slots for a plurality of wireless sensor nodes based on at least one channel quality metric, determining battery levels in each of the plurality of wireless sensor nodes and average battery level of all of the plurality of wireless sensor nodes, determining differences in battery level between each of the plurality of wireless sensor nodes and average battery level of all of the plurality of wireless sensor nodes, wherein if any such difference is above a predetermined threshold, increasing the transmission time slots allocation of wireless sensor nodes having higher battery levels relative to other wireless sensor nodes in the plurality of wireless sensor nodes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to wireless communication networks, and inparticular, wireless sensor networks.

2. Introduction

In many wireless sensor networks (WSNs) with star topology, all thewireless sensor nodes except the coordinator are battery powered. Thelifetime of such a network is given by the lifetime of the wirelesssensor nodes. There are two possible scenarios: (1) the network “dies”when the last wireless sensor node in the network “dies”, and (2) thenetwork “dies” when the first wireless sensor node in the network dies.Maximizing the average capacity of a network described in the firstscenario is a trivial exercise. Employing a “winner takes all” approach,the coordinator allocates all the available time slots to the wirelesssensor node that has the best channel capacity.

However, doing the same for a network considered in the second scenariois a complicated joint optimization problem. On one hand, the wirelesssensor nodes which have good channel capacity should be allocated asmany time slots as possible. However, doing so would disproportionallydrain the battery of those nodes. Therefore, it is desirable that allthe wireless sensor nodes in the network “die” at the same time. If thisgoal is not achieved, then energy resources in the network areunderutilized (i.e. there are nodes which can still transmit).

SUMMARY OF THE INVENTION

A method and apparatus that allocates bandwidth among wireless sensornodes in a wireless sensor network (WSN) is disclosed. The method mayinclude allocating transmission time slots for a plurality of wirelesssensor nodes based on at least one channel quality metric, determiningbattery levels in each of the plurality of wireless sensor nodes andaverage battery level of all of the plurality of wireless sensor nodes,determining differences in battery level between each of the pluralityof wireless sensor nodes and average battery level of all of theplurality of wireless sensor nodes, wherein if any such difference isabove a predetermined threshold, increasing the transmission time slotsallocation of wireless sensor nodes having higher battery levelsrelative to other wireless sensor nodes in the plurality of wirelesssensor nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 illustrates an exemplary diagram of a wireless sensor network inaccordance with a possible embodiment of the invention;

FIG. 2 illustrates a block diagram of an exemplary battery-aware dynamicbandwidth coordinator/wireless sensor node in accordance with a possibleembodiment of the invention;

FIG. 3 is an exemplary flowchart illustrating one possible battery-awaredynamic bandwidth coordination process in accordance with one possibleembodiment of the invention; and

FIG. 4 is an exemplary diagram illustrating time slot allocation inaccordance with a possible embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth herein.

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

The invention comprises a variety of embodiments, such as a method andapparatus and other embodiments that relate to the basic concepts of theinvention.

The invention concerns how to maximize the average network capacitysubject to also maximizing the lifetime of the network (i.e. all thewireless sensor nodes “die” at approximately the same time). Inparticular, the invention concerns the use of a channel quality metricand actual battery level of the nodes to maximize the average networkcapacity.

FIG. 1 illustrates an exemplary diagram of a wireless sensor network(WSN) 100 in accordance with a possible embodiment of the invention. Inparticular, the WSN 100 may include a battery-aware dynamic bandwidthcoordinator 110, and wireless sensor nodes 120, 130. The battery-awaredynamic bandwidth coordinator 110 may also be a node in the WSN 100.However, the battery-aware dynamic bandwidth coordinator 110 serves toallocate transmission times of the various wireless sensor nodes 120,130 in the WSN 100. While FIG. 1 only shows two wireless sensor nodes120, 130, this example is for ease of discussion as one of skill in theart may appreciate that more than two wireless sensor nodes (or aplurality of wireless sensor nodes) may exist in the WSN 100.

The battery-aware dynamic bandwidth coordinator 110 and wireless sensornodes 120, 130 may represent or be part of an electronicbattery-operated device in the WSN 100. For example, the battery-awaredynamic bandwidth coordinator 110 and wireless sensor nodes 120, 130 mayrepresent a mobile communication device. The mobile in a communicationdevice may be a portable MP3 player, satellite radio receiver, AM/FMradio receiver, satellite television, iPod, portable laptop, portablecomputer, wireless radio, wireless telephone, portable digital videorecorder, cellular telephone, mobile telephone, or personal digitalassistant (PDA), for example.

The WSN 100 may allow wireless sensor nodes 120, 130 to communicate withother wireless sensor nodes 120, 130, as well as the battery-awaredynamic bandwidth coordinator 110.

FIG. 2 illustrates a block diagram of either an exemplary battery-awaredynamic bandwidth coordinator 110/an exemplary wireless sensor node 120,130 in accordance with a possible embodiment of the invention. Since thebattery-aware dynamic bandwidth coordinator 110 is also a wirelesssensor node in the WSN 100, the exemplary structure shown in FIG. 2 mayapply to both an exemplary battery-aware dynamic bandwidth coordinator110 and an exemplary wireless sensor node 120, 130. For ease ofdiscussion, we will refer to the exemplary structure shown in FIG. 2 asa battery-aware dynamic bandwidth coordinator 110.

The battery-aware dynamic bandwidth coordinator 110 may include a bus210, a controller 220, a memory 230, an antenna 240, a transceiver 250,a communication interface 260, sensors 270, and a power supply 280. Bus210 may permit communication among the components of the battery-awaredynamic bandwidth coordinator 110.

Controller 220 may include at least one conventional processor ormicroprocessor that interprets and executes instructions. Memory 230 maybe a random access memory (RAM) or another type of dynamic storagedevice that stores information and instructions for execution bycontroller 220. Memory 230 may also include a read-only memory (ROM)which may include a conventional ROM device or another type of staticstorage device that stores static information and instructions forcontroller 220.

Transceiver 250 may include one or more transmitters and receivers. Thetransceiver 250 may include sufficient functionality to interface withany network or communications station and may be defined by hardware orsoftware in any manner known to one of skill in the art. The controller220 is cooperatively operable with the transceiver 250 to supportoperations within the WSN 100. The transceiver 250 transmits andreceives transmissions via the antenna 240 in a manner known to those ofskill in the art.

Communication interface 260 may include any mechanism that facilitatescommunication via the WSN 100. For example, communication interface 260may include a modem. Alternatively, communication interface 260 mayinclude other mechanisms for assisting the transceiver 250 incommunicating with other devices and/or systems via wirelessconnections.

Sensors 270 may include one or more sensors which detect, read, sense,etc. temperature, pressure, humidity, motion, vibration, sound, etc.,for example. The information generated from sensors 270 may be stored inmemory 230 and/or transmitted by transceiver 250 to another wirelesssensor node 120, 130, another network device, or the battery-awaredynamic bandwidth coordinator 110 (if the sensors 270 reside on awireless sensor node other than the battery-aware dynamic bandwidthcoordinator 110).

In the case of the battery-aware dynamic bandwidth coordinator 110, thepower supply 280 may represent either a DC (e.g., battery) or AC powersupply as the battery-aware dynamic bandwidth coordinator 110 may beeither DC or AC powered. However, with respect to wireless sensor nodes120, 130, the power supply 280 may represent a DC power source, such asa battery.

The battery-aware dynamic bandwidth coordinator 110 may perform suchfunctions in response to controller 220 by executing sequences ofinstructions contained in a computer-readable medium, such as, forexample, memory 230. Such instructions may be read into memory 230 fromanother computer-readable medium, such as a storage device or from aseparate device via communication interface 260.

The WSN 100 and the battery-aware dynamic bandwidth coordinator 110illustrated in FIGS. 1-2 and the related discussion are intended toprovide a brief, general description of a suitable computing environmentin which the invention may be implemented. Although not required, theinvention will be described, at least in part, in the general context ofcomputer-executable instructions, such as program modules, beingexecuted by the battery-aware dynamic bandwidth coordinator 110.Generally, program modules include routine programs, objects,components, data structures, etc. that perform particular tasks orimplement particular abstract data types. Moreover, those skilled in theart will appreciate that other embodiments of the invention may bepracticed in communication network environments with many types ofcommunication equipment and computer system configurations which operateoff of batteries, including cellular devices, mobile communicationdevices, portable computers, hand-held devices, portable multi-processorsystems, microprocessor-based or programmable consumer electronics, andthe like.

For illustrative purposes, the battery-aware dynamic bandwidthcoordination process will be described below in relation to the blockdiagrams shown in FIGS. 1 and 2.

FIG. 3 is an exemplary flowchart illustrating some of the basic stepsassociated with a battery-aware dynamic bandwidth coordination processin accordance with a possible embodiment of the invention. The processbegins at step 3100 and continues to step 3200 where the battery-awaredynamic bandwidth coordinator 110 allocates transmission time slots fora plurality of wireless sensor nodes 120, 130 based on at least onechannel quality metric. Many of the modern low-power radios, forexample, provide a measure of the quality of the communication channel.Two examples of measures of channel quality are the relative signalstrength indicator (RSSI) and link quality indicator (LQI). Severalstudies have shown that LQI is highly correlated with the packet errorrate (PER). Thus, to avoid the additional overhead of obtaining channelquality values, LQI may be used as the channel quality metric.

At step 3300, the battery-aware dynamic bandwidth coordinator 110determines the battery levels of each of the plurality of the wirelesssensor nodes and average battery level of all of the plurality ofwireless sensor nodes. The actual battery level (or capacity) may bedefined as the amount of charge the battery delivers under given loadand temperature conditions. The invention is independent of the batterytype and/or model. The average battery level of all of the plurality ofwireless sensor nodes is the total of all of the battery levels of thewireless sensor nodes divided by the total number of nodes in the WSN100.

At step 3400, the battery-aware dynamic bandwidth coordinator 110determines if any difference in battery levels between wireless sensornodes 120, 130 and average battery level of all of the plurality ofwireless sensor nodes in the WSN 100 exceeds a threshold. The thresholdmay be predetermined, based on lookup table, determined by a processaccording to environmental conditions, etc.

For example, assume that the battery level BL for wireless sensor nodesN₁ and N₂ are BL₁ and BL₂, respectively. If |BL₁-BL₂|≦e, then thewireless sensor nodes will be in an “equilibrium” state and thebattery-aware dynamic bandwidth coordinator 110 will dynamicallyallocate time slots proportionally to the channel quality of the nodes.

If the battery-aware dynamic bandwidth coordinator 110 determines thatany of the battery level differences between wireless sensor nodes 120,130 and average battery level of all of the plurality of wireless sensornodes exceed the threshold, then at step 3500, battery-aware dynamicbandwidth coordinator 110 increases the transmission time slotallocation of wireless sensor nodes 120, 130 having higher batterylevels. The process then returns to step 3300 immediately, or after adelay period, for example.

Thus, using the above two-node example, if |BL₁-BL₂|>e, thebattery-aware dynamic bandwidth coordinator 110 will allocate moretransmission time slots to a wireless sensor node 120, 130 that has ahigher battery level. This preferential treatment will be employed untilthe two wireless sensor nodes 120, 130 will again have their batterylevels within e of each other.

Stated it differently, this time slot adjustment will be done over aperiod of time that approximates similar average channel quality forboth nodes. As a result, both nodes will have, on average, approximatelythe same number of time slots allocated to each, and hence they will runout of battery at about the same time.

Mathematically, the number of time slots allocated to each node, NS_(i),can be expressed as Equation (1.0), below:

$\begin{matrix}{{NS}_{i} = \left\{ \begin{matrix}{\alpha + {\left( {{NTS} - \alpha} \right)*\left\lfloor \frac{{LQI}_{i}}{\sum\limits_{k = i}^{2}{LQI}_{k}} \right\rfloor}} & {{{if}\mspace{14mu}{BL}_{i}} > {BL}_{j}} \\{\left( {{NTS} - \alpha} \right)*\left\lfloor \frac{{LQI}_{i}}{\sum\limits_{k = i}^{2}{LQI}_{k}} \right\rfloor} & {{{if}\mspace{14mu}{BL}_{i}} \leq {BL}_{j}}\end{matrix} \right.} & (1.0)\end{matrix}$

where NTS is total number of time slots in a super-frame, and α is aparameter which is adjusted based on the |BL₁-BL₂| value. If|BL₁-BL₂|≦e, then α=0.

In the general case where there are N nodes in our battery-aware dynamicbandwidth allocation, the battery level of each node is compared to theaverage battery level of the N nodes

$\left( {{i.e.\mspace{14mu}{BL}_{avg}} = {\frac{1}{N}{\sum\limits_{j = 1}^{N}{BL}_{j}}}} \right).$The nodes, N_(k), whose battery level differences are greater than athreshold, e, will be allocated a fixed number of time slots, α_(k). Theremaining time-slots will then be allocated to the nodes according toEquation 1.1, below:

$\begin{matrix}{{NS}_{i} = \left\{ \begin{matrix}{\alpha_{i} + {\left( {{NTS} - {\sum\limits_{k}^{\;}\alpha_{k}}} \right)*\left\lfloor \frac{{LQI}_{i}}{\sum\limits_{j = 1}^{N}{LQI}_{j}} \right\rfloor}} & {{{{if}\mspace{14mu}{BL}_{i}} - {BL}_{avg}} \geq e} \\{\left( {{NTS} - {\sum\limits_{k}^{\;}\alpha_{k}}} \right)*\left\lfloor \frac{{LQI}_{i}}{\sum\limits_{j = 1}^{N}{LQI}_{j}} \right\rfloor} & {{{{if}\mspace{14mu}{BL}_{i}} - {BL}_{avg}} < e}\end{matrix} \right.} & (1.1)\end{matrix}$

If at step 3400, the battery-aware dynamic bandwidth coordinator 110determines that the battery level differences do not exceed thethreshold, the battery-aware dynamic bandwidth coordinator 110 proceedsto step 3600 where the battery-aware dynamic bandwidth coordinator 110determines whether the battery level is zero for all wireless sensornodes in the WSN 100.

If the battery-aware dynamic bandwidth coordinator 110 determines thatthe battery level in all the wireless sensor nodes is not zero (or“effectively” not zero), the process returns to step 3200 wherebattery-aware dynamic bandwidth coordinator 110 allocates transmissiontime slots for the plurality of wireless sensor nodes based on thechannel quality metric.

If at step 3600, the battery-aware dynamic bandwidth coordinator 110determines that the battery level is zero (or effectively zero) in allwireless sensor nodes 120, 130 in the WSN 100 (i.e., the network has“died”), the process goes to step 3700, and ends. Note that a node“dies” when its battery cannot support its normal operation. Therefore,as indicated above, while the battery level may not be exactly zero, itmay be effectively zero when its battery can no longer support thenode's normal operation.

FIG. 4 illustrates the time slot allocation process according to theexemplary process discussed above in relation to FIG. 3. From time T₀ totime T_(d)-1, the battery-aware dynamic bandwidth coordinator 110allocates time slots for the two wireless sensor nodes 120, 130proportional to their LQI values (parameter α in the equation above iszero). Because node N₁ has a better channel quality, the battery-awaredynamic bandwidth coordinator 110 allocates N₁ more transmission timeslots. As a result, its battery level goes down more rapidly then thebattery level of node N₂.

At time T_(d), the battery-aware dynamic bandwidth coordinator 110evaluates the battery level of the two wireless sensor nodes 120, 130.Since |BL₁-BL₂|>e, for the next super-frames, wireless sensor node N₂will be guaranteed a fixed number of time slots (2* in FIG. 4) inaddition to the ones the battery-aware dynamic bandwidth coordinator 110allocated to N₂ that are dynamically proportional to its channelquality.

After another T_(d) period, the battery-aware dynamic bandwidthcoordinator 110 again evaluates the battery level of the wireless sensornodes 120, 130, and since the battery levels are within e of each other,the battery-aware dynamic bandwidth coordinator 110 again allocates timeslots to the wireless sensor nodes 120, 130 proportionally to their LQIvalues.

The process can dynamically adjust the period over which the batterylevel is adjusted. This means that the overhead of the batteryestimation model is amortized over a dynamically variable number(usually large) of super-frames.

Embodiments within the scope of the present invention may also includecomputer-readable media for carrying or having computer-executableinstructions or data structures stored thereon. Such computer-readablemedia can be any available media that can be accessed by a generalpurpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to carryor store desired program code means in the form of computer-executableinstructions or data structures. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or combination thereof) to a computer, the computerproperly views the connection as a computer-readable medium. Thus, anysuch connection is properly termed a computer-readable medium.Combinations of the above should also be included within the scope ofthe computer-readable media.

Computer-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Computer-executable instructions also includeprogram modules that are executed by computers in stand-alone or networkenvironments. Generally, program modules include routines, programs,objects, components, and data structures, etc. that perform particulartasks or implement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of the program code means for executing steps of the methodsdisclosed herein. The particular sequence of such executableinstructions or associated data structures represents examples ofcorresponding acts for implementing the functions described in suchsteps.

Although the above description may contain specific details, they shouldnot be construed as limiting the claims in any way. Other configurationsof the described embodiments of the invention are part of the scope ofthis invention. For example, the principles of the invention may beapplied to each individual user where each user may individually deploysuch a system. This enables each user to utilize the benefits of theinvention even if any one of the large number of possible applicationsdo not need the functionality described herein. In other words, theremay be multiple instances of the battery-aware dynamic bandwidthcoordinator 110 in FIGS. 1 and 2 each processing the content in variouspossible ways. It does not necessarily need to be one system used by allend users. Accordingly, the appended claims and their legal equivalentsshould only define the invention, rather than any specific examplesgiven.

1. A method for allocating bandwidth among wireless sensor nodes in awireless sensor network, the method comprising: allocating a portion oftransmission time slots for a plurality of wireless sensor nodes basedon at least one channel quality metric; determining battery levels ineach of the plurality of wireless sensor nodes and average battery levelof all of the plurality of wireless sensor nodes; allocating a remainingportion of transmission time slots for the plurality of wireless sensornodes based on the determined battery levels; and determiningdifferences between the battery levels of each of the plurality ofwireless sensor nodes and the average battery level of all of theplurality of wireless sensor nodes, wherein if any such difference isabove a predetermined threshold increasing the transmission time slotsallocation of wireless sensor nodes having higher battery levelsrelative to other wireless sensor nodes in the plurality of wirelesssensor nodes.
 2. The method of claim 1 wherein if any difference inbattery levels is not above a predetermined threshold, then allocatingtransmission time slots for a plurality of wireless sensor nodes basedon at least one channel quality metric.
 3. The method of claim 1 whereinthe at least one channel quality metric is at least one of a linkquality indicator and a relative signal strength indicator.
 4. Themethod of claim 1 wherein the difference between the battery levels ofeach of the plurality of wireless sensor nodes and the average batterylevel of all of the plurality of wireless sensor nodes is determined atpredetermined times.
 5. The method of claim 1 wherein one of theplurality of wireless sensor nodes serves as a battery-aware dynamicbandwidth coordinator and allocates transmission time slots to the otherwireless sensor nodes in the wireless sensor network.
 6. The method ofclaim 1 wherein each of the plurality of wireless sensor nodes transmitssensor information, the sensor information being at least one oftemperature, pressure, humidity, motion, vibration, and sound.
 7. Themethod of claim 1 wherein each of the plurality of wireless sensor nodesis part of a mobile communication device, the mobile communicationdevice being one of a portable MP3 player, satellite radio receiver,AM/FM radio receiver, satellite television, iPod, portable laptop,portable computer, wireless radio, wireless telephone, portable digitalvideo recorder, cellular telephone, mobile telephone, and personaldigital assistant.
 8. An apparatus that allocates bandwidth amongwireless sensor nodes in a wireless sensor network, the apparatuscomprising: one or more sensors that sense environmental conditions; atransceiver that transmits sensor information related to the sensedenvironmental conditions using transmission time slots; and a controllerthat allocates a portion of the transmission time slots for a pluralityof wireless sensor nodes based on at least one channel quality metric,determines battery levels in each of the plurality of wireless sensornodes and average battery level of all of the plurality of wirelesssensor nodes, allocates a remaining portion of transmission time slotsfor the plurality of wireless sensor nodes based on the determinedbattery levels, and determines the difference between the battery levelsof each of the plurality of wireless sensor nodes and the averagebattery level of all of the plurality of wireless sensor nodes, whereinif any such difference is above a predetermined threshold, thecontroller increases the transmission time slot allocation of wirelesssensor nodes having higher battery levels relative to other wirelesssensor nodes in the plurality of wireless sensor nodes.
 9. The apparatusof claim 8 wherein if any difference in battery levels is not above apredetermined threshold, then the controller allocates transmission timeslots for a plurality of wireless sensor nodes based on at least onechannel quality metric.
 10. The apparatus of claim 8 wherein the atleast one channel quality metric is at least one of a link qualityindicator and a relative signal strength indicator.
 11. The apparatus ofclaim 8 wherein the controller determines the difference between thebattery levels of each of the plurality of wireless sensor nodes and theaverage battery level of all of the plurality of wireless sensor nodesat predetermined times.
 12. The apparatus of claim 8 wherein theapparatus serves as a battery-aware dynamic bandwidth coordinator whichallocates transmission time slots to the other wireless sensor nodes inthe wireless sensor network.
 13. The apparatus of claim 8 wherein thetransmitted sensor information is related to at least one oftemperature, pressure, humidity, motion, vibration, and sound.
 14. Theapparatus of claim 8 wherein the apparatus is part of a mobilecommunication device, the mobile communication device being one of aportable MP3 player, satellite radio receiver, AM/FM radio receiver,satellite television, iPod, portable laptop, portable computer, wirelessradio, wireless telephone, portable digital video recorder, cellulartelephone, mobile telephone, and personal digital assistant.
 15. Amobile communication device comprising: one or more sensors that senseenvironmental conditions; a transceiver that transmits sensorinformation related to the sensed environmental conditions usingtransmission time slots; and a controller that allocates a portion ofthe transmission time slots for a plurality of wireless sensor nodesbased on at least one channel quality metric, determines battery levelsin each of the plurality of wireless sensor nodes and average batterylevel of all of the plurality of wireless sensor nodes, allocates aremaining portion of transmission time slots for the plurality ofwireless sensor nodes based on the determined battery levels, anddetermines the difference between the battery levels of each of theplurality of wireless sensor nodes and the average battery level of allof the plurality of wireless sensor nodes, wherein if any suchdifference is above a predetermined threshold, the controller increasesthe transmission time slot allocation of wireless sensor nodes havinghigher battery levels relative to other wireless sensor nodes in theplurality of wireless sensor nodes.
 16. The mobile communication deviceof claim 15 wherein if any difference in battery levels is not above apredetermined threshold, then the controller allocates transmission timeslots for a plurality of wireless sensor nodes based on at least onechannel quality metric.
 17. The mobile communication device of claim 15wherein the at least one channel quality metric is at least one of alink quality indicator and a relative signal strength indicator.
 18. Themobile communication device of claim 15 wherein the controllerdetermines the difference between the battery levels of each of theplurality of wireless sensor nodes and the average battery level of allof the plurality of wireless sensor nodes at predetermined times. 19.The mobile communication device of claim 15 wherein the transmittedsensor information is related to at least one of temperature, pressure,humidity, motion, vibration, and sound.
 20. The mobile communicationdevice of claim 15 wherein the mobile communication device is one of aportable MP3 player, satellite radio receiver, AM/FM radio receiver,satellite television, iPod, portable laptop, portable computer, wirelessradio, wireless telephone, portable digital video recorder, cellulartelephone, mobile telephone, and personal digital assistant.